Angiotensin II (Ang II) acts via neuronal Ang II type 1 receptors (AT1-R) within the brain to increase sympathetic outflow and blood pressure, and hyperactivity of these effects plays a major role in hypertension. Thus, factors that regulate the neuronal actions of Ang II in the brain will modify the effects of this peptide on blood pressure. The current proposal focuses on the role of macrophage migration inhibitory factor (MIF) as a possible intracellular regulator of these neuronal actions of Ang II, in particular at the paraventricular nucleus (PVN), a center for control of sympathetic outflow and blood pressure. Based on preliminary findings we have developed the novel hypothesis that MIF, produced within neurons in response to Ang II, acts as a chronic intracellular negative feedback regulator of Ang II's chronotropic actions. Specifically, the proposal is that: (i) In normotensive rat neurons MIF, produced in response to Ang II, exerts an inhibitory influence which dampens or prevents further stimulatory actions of Ang II on neuronal firing; (ii) MIF inhibits the neuronal chronotropic action of Ang II via it's thiol-oxidoreductase activity, scavenging of reactive oxygen species (ROS) and modulation of membrane K+ and Ca2+ currents; (iii) In normotensive rat PVN, Ang ll-induced increases in MIF expression serve to blunt or depress subsequent increases in sympathetic outflow and blood pressure elicited by Ang II. In this proposal our overall goal is to investigate a novel role of MIF as an inhibitor of Ang ll-induced responses in neurons. The above hypotheses will be tested through in vitro and in vivo studies that will combine cellular, molecular, gene transfer and physiological approaches. The specific aims are: (1) Investigate the role of MIF as an inhibitor of the chronotropic action of Ang II in neurons; (2) Investigate the intracellular mechanisms by which MIF affects the neuronal chronotropic actions of Ang II; (3) Determine the consequences of increased MIF expression in the PVN to Ang ll-induced cardiovascular effects. These studies will establish a role for MIF as an inhibitory regulator of the CNS actions of Ang II on sympathetic outflow and blood pressure, and will lay the groundwork for determining whether a lack of this MIF regulatory mechanism contributes to hypertension.